Browsing by Author "MacInnis, Martin J."
Now showing 1 - 5 of 5
Results Per Page
Sort Options
- ItemOpen AccessDecrements in Cycling Performance are Dependent on the Intensity and Duration of Prior Exercise(2020-08-31) Fullerton, Madison; Murias, Juan M.; Passfield, Louis; MacInnis, Martin J.; Aboodarda, Saied JalalThe maximal lactate steady state (MLSS) is a physiological model that can be used to delineate the heavy- from the severe-intensity domain of exercise. The importance of this threshold has been repeatedly demonstrated, as it differentiates intensities that result in stable physiological responses from those that progress towards maximal values. To understand the implications that exercise performed at this intensity has on subsequent performance, a recent study demonstrated that time-to-exhaustion (TTE) performance is reduced following prior exercise performed at the power output (PO) corresponding to MLSS (MLSSp) and reduced even further following a small (i.e., 10 watt (W)) increase above MLSSp. Therefore, the purpose of this thesis was to determine whether submaximal intensities (i.e., sub-MLSSp) as well as different durations at MLSSp would have any impact on subsequent TTE performance, within the severe-intensity domain. The results from this thesis demonstrated curvilinear and linear reductions in TTE performance following increase in the intensity and duration of the preceding bout of exercise, respectively. These results highlight that the capacity within the severe-intensity domain is dependent on both the intensity and duration of a prior bout of exercise. Moreover, these findings also illustrate the importance of properly determining thresholds and the exercise intensity domains on an individual basis, as small changes in the PO surrounding MLSS have detrimental effects on performance. Lastly, this thesis also highlighted the importance of perceptual responses during exercise. Rating of perceived exertion (RPE) was associated with the reduction in TTE performance for both the intensity and duration conditions, indicating that the capacity within the severe-intensity domain can be estimated by RPE assessed immediately prior to each TTE trial.
- ItemOpen AccessThe effect of simulated altitude on VO2max in humans(2019-11-19) Zhuang, Andrea Y.; Beever, Austin T.; MacInnis, Martin J.
- ItemOpen AccessLocomotor biomechanics and behaviour in the ocellate river stingray(2020-04-22) Seamone, Scott G.; Syme, Douglas A.; Bertram, John Edward Arthur; Post, John R.; Standen, Emily M.; MacInnis, Martin J.Stingrays are fishes that are dorsoventrally flattened in the same plane as the substrate, similar to a hydrofoil, with long thin tails that have an absent or reduced caudal fin, and anterior to the pelvic girdle the longitudinal body axis is relatively rigid. These characteristics would appear to constrain or preclude many of the locomotor behaviours that are employed by fishes that typically swim via undulations of the longitudinal body axis and caudal fin, and which tend to dominate descriptions of fish swimming in the literature. In contrast, stingrays exhibit a variety of locomotor behaviours powered via enlarged and flexible pectoral fins that wrap around the body and head (i.e. the pectoral disc), yet an in-depth understanding of the biomechanical mechanisms that permit these behaviours has not been formed. Potamotrygon motoro, the ocellate river stingray, lives along the substrate in a benthic environment, and possesses an extremely rounded pectoral disc, from the dorsal view. It is used in these studies to represent the flattened shaped, low profile, and relatively rounded disc common to benthic stingrays, to better understand how these animals achieve different locomotor behaviours. The studies described in this thesis offer insight into how the shape of P. motoro is employed to accomplish behaviours exhibited by many benthic stingrays such as fast-start maneuverability, station holding and burying. Chapter 1 reviews our current and somewhat limited understanding of how shape impacts swimming behaviour in fishes that are flattened in the same plane as the substrate, described here as foil fishes, and explores relationships of shape and ecology observed in stingrays. Chapter 2 describes studies where video analysis was used to reveal that flexibility in the movements of the pectoral fins around the flattened and nearly symmetrical disc shape permits fast-start escape in all directions across the benthic plane with similar performance, regardless of initial orientation of the fish, which appears to challenge the conventional description of maneuverability typically used to evaluate fishes. Chapter 3 describes studies where recordings of changes of pressure beneath the pectoral disc, and video observations of movements of dye, are used to argue that stingrays can exercise movements of the body and fins to flush water from beneath the ventral surface to create and maintain a seal between the pectoral disc and benthos, to achieve suction pressures via a vacuum and possibly Stefan adhesion, that can resist an upwards displacing force to hold station along the benthos. Chapter 4 describes studies that used video analysis and particle image velocimetry to explain how rapid and vigorous movements of the body and fins in stingrays fluidize and suspend vortices of sediment below the ventral surface of the fins, which are then directed up and over onto the dorsal surface to cover the fish with sediment and effect burying, and that the fish appear to direct and control these vortices to modulate the extent and pattern of burying. Chapter 5 describes studies that used time-lapse photography and video analysis to reveal that in the presence of sediments that differ in grain size, stingrays mostly choose to inhabit and bury in finer grained sediments when threatened, and this appears to reflect these fishes being more effective at burying in finer sediments, such that the rate of coverage of the dorsal surface is faster for a given finbeat speed. Chapter 6 provides a summary of what has been revealed by these studies, conclusions and future directions. These studies advance our understanding of how a flattened and rounded disc shape in P. motoro might find success in a benthic environment, and might inspire engineers interested in fish for the design of underwater robotics.
- ItemOpen AccessMenstrual and Oral Contraceptive Phases Do Not Influence Submaximal and Maximal Responses to Exercise or Vascular Responsiveness at Rest(2020-04-20) Mattu, Anmol Trishia; Murias, Juan M.; MacInnis, Martin J.; Doyle-Baker, Patricia K.Endogenous and exogenous female reproductive hormones fluctuate across the respective menstrual and oral contraceptive cycle phases. Importantly, estrogen and progesterone are known to have numerous physiological effects, which are likely to have an impact on exercise outcomes. Current literature exploring the effects of the menstrual and oral contraceptive cycles on exercise responses is limited and remains inconclusive (1). Moreover, no previous studies have examined the within-cycle effects on muscle microvascular function at rest, which may provide important insight into the changes in oxygen delivery to active tissues during exercise across the cycle phases. Therefore, the objective of this thesis was to examine whether the menstrual or monophasic oral contraceptive cycle phases affect a wide variety of submaximal (oxygen uptake (V̇O2) kinetics, maximal lactate steady-state (MLSS)) and maximal (maximal oxygen uptake (V̇O2max), time-to-exhaustion (TTE)) responses to exercise, and vascular responsiveness of the lower limb microvasculature at rest in healthy, active women. During the follicular or inactive-pill phase and the luteal or active-pill phase of the menstrual or oral contraceptive cycle, respectively, 15 non-oral contraceptive users and 15 monophasic oral contraceptive users underwent a lower limb vascular occlusion test and performed one V̇O2 kinetics test; one ramp-incremental test to exhaustion; two to three 30-min constant-load cycling trials to determine the power output corresponding to MLSS, followed by a TTE trial. Menstrual cycle phases were verified using an ovulation test. Vascular responsiveness was assessed by calculating the near-infrared spectroscopy-derived muscle oxygen saturation (StO2) reperfusion slope and the post-occlusion StO2 area under the curve of the tibialis anterior muscle. The results suggest that the fluctuations of natural or synthetic hormones between the phases of the menstrual or oral contraceptive cycle, respectively, had no detectable effects on submaximal (V̇O2 kinetics, MLSS) and maximal (V̇O2max, TTE) exercise performance and lower limb microvascular reperfusion responses. Future research studies evaluating exercise performance or microvascular reperfusion should not avoid testing women solely based on the idea that the cycle phases may act as a confounding variable for their outcome measures.
- ItemOpen AccessRyanodine Receptor Modifications Following Sprint Interval Exercise: Time Course and Fibre-Specific Responses in Human Skeletal Muscle(2021-01-07) Tripp, Thomas R.; MacInnis, Martin J.; Murias, Juan M.; Shearer, JaneIt was recently discovered that a single session of sprint interval training (SIT) resulted in fragmentation of the sarcoplasmic reticulum calcium (Ca2+)-release channel, ryanodine receptor 1 (RyR1), leading to an increase in intracellular [Ca2+], a known signal for mitochondrial biogenesis; however, it was unclear whether fragmentation could initiate mitochondrial biogenesis, as RyR1 fragmentation had only been observed 24 h post-exercise in humans, and most signalling events occur much earlier. The primary objective of this thesis was to characterize the time course of RyR1 modifications following SIT in whole muscle and pooled type I and type IIa muscle fibres in humans. The secondary objective was to assess if SIT affected the content of other Ca2+-handling proteins alongside RyR1. We collected muscle biopsy samples from recreationally-active males (n = 6) and females (n = 4) before and 3 h, 6 h, and ~24 h after they completed a single session of SIT (6 x 30-s ‘all-out’ with 4.5 min rest). Western blotting experiments showed that full-length RyR1 content was significantly lower at 6 h (-44 ± 31%; p = 0.01) and 24 h (-35 ± 42%; p = 0.02) compared to pre-exercise. RyR1 content was also lower than pre-exercise at 6 h in type IIa fibres (-21 ± 17%; p = 0.01) but not type I fibres (-2 ± 43%; p > 0.05). Aside from FKBP12, which was higher at 24 h compared to 3 h (26 ± 29%; p = 0.03) and 6 h (24 ± 23%; p = 0.03), Ca2+-handling protein content was stable in whole muscle (all p > 0.05). Our results indicate that RyR1 fragmentation is fibre type-dependent and occurs on a similar time course to other relevant signalling events reported elsewhere in the literature. RyR1 fragmentation, in conjunction with stable content of other Ca2+-handling proteins, supports previous work suggesting a post-SIT increase in intracellular [Ca2+] is primarily due to RyR1-related Ca2+ leak. Overall, this thesis supports a role of RyR1 modifications in triggering mitochondrial adaptations in response to sprint interval training.